Anti-ringing limiter



Nov. 24,l v1959 R. L.. TERRY 2,914,683

V ANTI-RINGING LIMITER v Filed Aug. Ae, 195e 12 sheets-sheet 1 I 14 fz14H fdl-L Zener dinde farwdrdv /a//f faer/ L, A??? Nov;l 24, 1959 FiledAug. 6, 1956 R. L. TERRY ANTI-RINGING LIMITER .'2 Sheets-Sheet 2lll/ern? y 2,914,683 iANri'tRmGnftGLu/HTER Y LL. Terry,.Los.Angeles,Calif., assignor'to Litton Industries otv California, Beverly Hills,

s claims." (ci. 307-885) invention relates "to pulse limiting anddamping, fcircu-its and more particularly to `an anti-ringing limiterrfor clamping Vat a'predetermined value'the amplitude of'lavoltagep'ulse obtained 'across-an inductor circuit'in refsponse toacurrent pulse passed therethrough and for damping the'inductor"cifrcuit toeliminate -undesirable hsubsequent ringing voltagepulses. 1 Y

It isknown that "wheneverjafsingle current pulse `is .forced through aninductor, -there results a rst polarity Voltage'pulse in response togtherise' and a second opposite polarityvoltage pulse'in response to thefall of thecurrent pulse. Due to lthe distributed and 'Straycapacitance, winding resistance,` and '-fcoreldsses associated with* any'inductor, the Aresulting LCR circuit Y,willfring ase'vidence'd v by thegeneration of succeeding alternatepolarityvoltages pulses of diminishingamplitude which continue until the energy introduced by the currentpulse is dissipated by the resistance of the circuit. p y l-In manyapplications fof linductory circuits 'in electronic -iequipin'en` suchvlas blocking oscillators `and transformer ,United ,States Patent2,914,683 lPfa`.t`enterl v Nov. 24, 11959 current ow through ftheforward-biased diode and lowV Y `currentpulsepassing'through theVinductor'of thecircuit 'circuits fto'substantially "eliminateundesirablefringing pulses which tend to develop across the inductorsin'responsevtoeach currentpulse passing therethrough." In suchFapplicationgfit lis Afrequently also delsiifabl'ef tof-limit theamplitude ofthe` desired pulse, hereinafter sometimes- 'referr'edto asthe primary pulse, developed across ithe-inl dctor byeach current pulsetofa predeterminedflixd yvalue by a suitable clamping circuit.

1 Since the am und -1argesfu1up1itudeuiugiug pulsfccur- -rin'g across aninductor isk opposite Kinrlpolarity to the primary'jpulse ani'nductorcircuit :may be appropriately 'clamped l by shunting Vthe' inductr "byfa`@resistor of proper magnitude andf'a unidirectional current device forcon- Iven'tionalidiode l'connected in series. `By vproperlypoling` thediode,-?it"will bfe' back-biased :by the 'primary pulses vAla'nfdfoifwarc1-biased `by -the lirst 'ringing lpuls'e following f ylp'rimar'y `pulse 'whereas the ringing 'pulse following leach primarypulse produces a current flow throughth'e resistor v thus-substantiallydissipatiug the energyremiuihgtiu the riieto'r. :Y Y

ringing pulses'hom "developing across jan 'iductor' circuit. *Auditiuualeircuitryphpwever, Vis required tu ljurfthe amplitude, of thedesired-'Pp m'ary pulse'sto la desired determined val-1re. *Inthefprioir fart, diodeclampi i cuits {ae fgeerally utilized tolirnitftliearrijgilitudevo e desired output pulses. w'A diode clampingcircuit, `iu fits suit-pleut form, uequires "l-16W uupedau gputuutiuscure@ :andv azdiede- Th'euw- 'impedance potential -sjurce is -fselected'to de'velo`p Aai"cons'tant D.C. "p'tential," referred to la.' low?impedance and at the same time avoid the development of undesirableringing pulses, 'two-separate circuits are necessary. First, some form'of Adamping'circuit,"such asthe series dioderes'istor' circuitabovedescribed, iis V`necessary to critically 'dampen the'inductor circuit.Second, a separate clamping -circuit includingfasecondhdiode and a lowimpedance D'.C. poteuti'al source isue'eded to clauipthe A'amplimdefof`the output pulse. at thepredeterniined desired level. V"Byfar themostFundesirable "featureof the prior ar't `damping andiclamping circuitryabove ldescribeizl "the 'necessity' 'for "developingclampiiig voltagesfrom ia vlori' "impedance-sourczeiv flu-order to accurately clampthe-de# sired"output `pulses, 'at a predeterrrinedl amplitude,l twolsurceg: First, in forderj tosha'rply crit-"off, the amplitude ofvoltage source inust provide n u pathtor current' conduteduhruugh-uheualupiug `drague' when the' lltter isffuuu biased.'Secondlyftlie claiping voltage "source vmus very accurately regulated'to provide `theexact desired clamping voltage at allftimes `irrespectiveotjch'anging load.' -It shouldv be fu'rth'er understood thatif; (pas isusually th'e-case) rthe induc'tor'referenced `to some 'volti age otherthan "groundyit i s necessary to regulate this `reference voltage as wellas ftheclainping voltage for` any relative"changebetwen vthe`clr'npi'ng-"voltage,and the p reference :voltage 'wiIlcause Variationsin pulsamplitude even" thoughY :the absolute 'fvalueo'f clamping voltageremains unchanged?) *1 1Iiir'elatively cmplxelectrnic eduip "'r'1t, asradar and digital computing apparatus, wherein a multi fthe devlopmentofLsuitable cla'mpingyltages 'forfclarrip-Y ing voltage pul'sesgeneratedacross the inductors. Within th'e equipment,"mayreqnireconsiderablecircuitry. Be- Yca'use`fof the'requied 'lowimpedanceandfhigh regulationv of :the clamping "voltage source,"'tliefclamping'voltage Y dVIpd t iIt is also an object of tlieppresentinvention to'provid as a clampingvoltage, equal to thedesired amplitude' ihit coupled to the-indctor'circuit by 'the diode in "a Amanner whereby the diode is back-biased solong as the amplitude current pulse forced th" source may representafsbstatia'lfportioriof an electronic apparatus. *The problem is'ecially?complexfwhereva variety yof ditferentfvaluedfclarnpmg'voltagesare required to'clampith'e amplitude offvolta'ge signalsdevelop'edacrossA spundiug1yfdifferentamplituderevus.` y u lAccordingly, itis fan object of 'the preser'itfinvention to a number ofinductors Within a single machine `altcorfr'eprovidefanantiiringinglimiter, which 1does not f equireha'` Y cllmpingvoltage*potential silcelthe limiter 'clamping at a Vpredetermined levelvthe amplitudey of avoltage developed across *an inductorkirciiitiin'response to a opgh, and`damping thenin "prevent nde'sir'e'd `ringing;i pulses` "from ductor:=circuit #LA rurtherobje'et offthe' present-'invention is to providemodified anti-ringing limiter circuit inaccorlance with the i: .To2,914,683

sponse to the same current pulse is` obtained without the necessity forgenerating a separate clamping voltage by shunting the inductor with aresistor and a Zener diode connected in series. A'Zener diode, as iswell-known in `the art, has the characteristic ofbecoming stronglyconductive at a xed, predetermined back-bias breakdown voltage referredto as the Zener voltageof 'the diode. Whenever the back-bias v oltage`acrossthe Vdiodetends ,toincrease beyond the Zener voltage, aback-current is passed through the diode which tends to. prevent furtherincrease of the back voltage.' :E r.

Theseries circuit comprisedfof theresistor' andfZen'er Vdiode isvconnected acrossan inductorV in a manner .to Vcausethe Zener diodetoghe, back-biased by each desired primary voltage `pulse developed`across the inductor and forward-biased by the subsequent oppositepolar'ity' ringfing pulse following eachA primary pulse. :Thus theinvductor may beappropriately damped` (preferablyicritically damped) bypassing through the Aresistor whichhas a predetermined resistancemagnitude 4chosen sof as to furnish the desired damping, therebydissipatingenergy `stored in the inductor. in vresponse to arringingpulse, yet isolating the resistor from the inductor as each desiredprimary pulse developed across the inductor;V -When .the amplitude of adesired primary pulse exceeds the YZener voltageof the diode,' onV theother hand,l a backd current-flows through the diode and thence throughthe resistor thereby substantially limiting the amplitude of eachdesired voltage pulse to the Zener voltage ofthe diode.. ByV the properselectionl of al Zener diode, any desired Zener voltage and hence anydesired amplitude of ,the output pulses may be obtained. i To furtherimprove the amplitude limiting action of the anti-ringing limiter of thepresent invention, it may be desirable to shunt the Zener diodeback-current, around the resistor. To accomplish this it is merelynecessary kto vshunt the resistor by-aconventional unidirectionalcurrent'devlce, Le. a conventional diode whichis forward- VbiasedVbythe'desired primary voltage pulses.r :Backcurrent passing through theZener diode [.is thereby shunted around n the resistor through the,forwardfbiased eoInventionaldiode.V v 'Y Y r i.

` :The novel features which are believed to be characten istic ,of theinvention, both as to its organization and methodk of loperation,together. with l further objectsl and advantagesthereof, uwill be betterunderstood from the frc'pllovvingV description considered in connectionwith the accompanying drawings in which severalembodimen-ts of theinvention are illustrated by `way of example. AIt is to be expresslyunderstood, howeventhat the drawings are Iier stage for limitingpositive output pulses produced in the inductor;

Fig. 5 is a waveform chart illustrating the nature of the pulse signalsappearing at various points in the circuitry illustrated in Fig. 4.

Referring to Fig. l, there is schematically presented an embodiment ofan anti-ringing limiter in accordance with the present invention, thelimiter being shown as being adapted for operation in conjunction with atransformer coupled amplifier stage including an amplilier element -2,supplied with power from a B+ supply, not shown, through a primarywinding 3 of a transformer 4. Am-

pliter 2 is `responsive to application of` a positive input pulse fordeveloping across a secondary 5 of transformer 4, a positive outpu pulserepresenting an amplified red plica of the input pulse, the amplitude ofthe output pulse being limited to a predetermined maximum value. Although amplier element 2 may be any type of amplifier o element such asa vacuum tube, diode amplifier, etc., as

for lthefpurpose of illustration and description only, and

arey not int'endc'e'dA las a definition ofthe limits offthe invention.,p A, Fig. l is a schematic circuit diagram of an embodiment oftheantifringing limiter of the present invention illustrated inconjunction Vwithan;inductorfloaded ampliiier stage for .limiting jnegative 'pulses produced in the inductor; 7,-, Fig. YZbis a graphVillustrating the voltage current characteristics of atypicalZener-,diode;vv

YFig. 3.isa.waveformfchartfillustrating the; nature of the pulse signalsappearing at various points inthe circuit ifFig- 1; n `j o. f Y

4 is a schematic circuit diagram rof :an `,embodiment of theanti-ringing limiter circuitjof the present invention illustrated inconjunction with` an inductor-loaded amplishown in Fig. l amplifierelement 2 is illustrated as an NPN type transistor having itscollectorconnected to a `lower terminal 8 ,of primary winding 3 and its emitterconnected to a source of ground potentiaLthe positive input pulse beingapplied to the base region of the transis tor. Since upper terminal9 of primary; Winding 3 is con nected, as illustrated, to the B+ supply,a positive input pulse causes a corresponding positive current pulse tobe forced through primary winding 3;

Consider rst the case where the anti-ringing limiter circuit 1 isdisconnected from primary'winding 3. Since the voltage signals appearingacross winding 3, in response to a single current pulselpassingtherethrou-gh,-.are a function of y Ldt a negative 'voltage-v pulse willbe developed'across the winding in response-tothe leading or rising edgeof the current' pulse and a subsequent'positive voltage pulse will bedeveloped acrossthe winding: inl response to Atheffalling or trailingedgeof the current pulse. Fur- `ther,1 due to .v the distributedIcapacitance of winding 3 and additional unavoidablestray capacitanceexisting between the remainder of the amplifier-'stage and ground, theresultingV LC circuit lwill ring.due=to oscillation of energy-betweenthe inductance and ycapacitance of the circuit. As a consequence,alternate positive and nega- .tivervoltage pulses` are. developed acrosswinding 3 until the energyointroduced into the winding by the singlecurrent pulse is dissipatedrin the resistance of thecircuit. It isdesired, however, to produce but a single posi- .tive output pulsehaving a predetermined amplitude, across secondary winding 5 of thetransformer'in response to positiveinput pulse appliedl to amplier 2.Accordd ingly, `it isnecessary both to limit the amplitude 'of thenegative pulse across winding 3 to a predetermined value and also todamp the winding for the subsequent positive ringing pulse to therebysubstantially eliminateringing signals in the winding.

The above objectives are accomplished by connecting output leads 11 and10 of the anti-ringing limiter 1 of the lpresent invention to terminals8 and 9, respectively, of

winding3 as illustrated.4 Anti-ringing limiter 1 includes a Zener diode12 Vhaving itsranode connected byI aconductor llrtoterminal rofwinding 3and :having its cathode connected `to one endy of-,a damping resistor 13whose other end is connected by. a conductor 10 to the other terminal 9of winding 3. Itis clear thata seriesdiode-resistor circuit istherebyestablished across winding 3. Asshown in Fig. l, Zener diode12ris poled so that it is back-biased bythe'desiredy negative primarypulse appearing across winding 3 and forward-biased by the succeedingpositive ringing pulse. v

When a positive current pulse is forced through win ing 3in response toapplication of a positive input voltvalue of thev Zener voltage.

Y Scale of thetabsciss-a.

r"ageipulse', the'negative (primary) voltage pulse, develropedeacrosswinding`3 inresponse to' the rise of the current,pu1se,.back`-biasesdiodelZ. `As a-result, resistor 13 isisolatedifrom winding '3a-at thistime. The succeedingA positiveringing-jpulse forward-biases diode 12 andvthus permitscurrentlflow through thefdiode and thence through 'resistor13.` As a result, by the proper choice y Yof .resistance-.value for`resistor 13, theenergy introducedV in winding 3 byr-the currentpulsemayibe substan- `tially dissipatediin the resistor so thatundesired ringing "pulses'maybedamped to any extent desired.

y.Consider nowthe operation of anti-ringinglimiter f1 `when .a desirednegative voltage pulse appearing 4across winding S3 exceeds in amplitudethe Zener yvoltageof Zener diode l121. `When this ocoursfZener diode 12v breaks Adown. and permits ai back-current to flow through diode12`fa`nd thencethroug'liresistor 13. Amplier 2 4now operates into a'much`lower impedance than was the case when the transformer 4 andanyexternal fpedance connected thereto represented theonly load onacross` winding f3, the increase in current being shuntedv asf-aback-current through Zenendiode 12 and thence through resistor 13. Asy aresult, the amplitude of the negative voltagejpulse is Vsubstantiallymaintained at the VIt-may happen that `the value winding 3 may ybe tooVlarge to permit suicient `back- `of resistor -13 requiredv torappropriately damp theinductive `circuit of primary current owthrough`Zener diode 12 for sharply limiting i vthe `amplitude'of the desired`negative voltage pulses 'at the predetermined Zener voltagelevel. Inthis -case it is 'desirable to'shunt resistor 13 by a conventional diode:'14las Ashown--finFigV v1,diode 14 having a polarity asindicated-'sothat it lisforward-biased bythev desired negative voltage pulses "to"provide'a low impedance path yaround resistor 137for the :baclocurrentof Zener. diode 12. t uAsan aid'toa clearunderstanding ofthe operationof Zener diode 12of' Fig. `1, reference is brieiiy made to Fig. 42wherein there is presented a-graph ofthe voltagecurrent characteristicofatypical Zener diode. Inthe graph, forward-bias'voltages are scaledalong the abscissa ofthepgraph to theright and back-bias voltages to theleft of the ordinate. "Corresponding forward and back currents arescaled on the ordinate .of the graph above and below"the` 'abscissa,respectively.` The voltage-cur# rent characteristic of atypicalZener-diode is represented in :the graph b y aheavy line solabeled. The Zener or ;back-bias ybreakdown voltage-of the `diode isVindicated byanarrow along a portion `,off the-back-bias voltage The-nature of the pulse signals appearingat various points `in, Vthecireuitof P ig. lin response to `,two successive positive input pulsesdesignated E1n, are presented `in the waveform chart of Fig. 3 whereinthe actual sig nals appearing at the corresponding points of the circuitare illustrated by solid lines and the signals which would appear atthese points were the `anti-ringing limiter 1 removed from the remainderof the circuit are'indicated -by dotted lines. The reference voltage ofeach waveform is indicated just to the right of the symbol identifyingthe waveform.

' Considering briey the waveforms of Fig. 3, each positive inputpulse Emcauses a corresponding positive current puise to be forced throughprimary winding 3. For purposes of illustration, only the magnetizationcurrent pulses Ip are shown. It should be understood however, that theresultant current pulse developed by yamplifier 2 in response to eachinput voltage En, includes a magnetization and a transformerload currentcombined to produce a single currentpulse through winding 3. Additionalcurrent supplied by amplifier 2 will be shunted through diode 12 andresistor 13.

to the inductor for limiting the amplitude of the first 'of Fig. llis.indicated 'by the solid lines wherein the amplitude of veach ofthedesired negative pulses is substantially limitedto the Zener'volta'geEb, of Zener diode 12, and thepositive ringing pulses are substantiallyeliminated.

The output voltage pulses Bouty appearing across sec,- ondary winding 5,ofthecircuit of Fig. 1 are indicated by'solid 'lines in the waveformchart of Fig. 3. The output'pulsesfEou,i which would appear in theabsence of t anti-ringing limiter are represented in the waveform chart,

as before, by'dottedlines.

`Referring 'to Fig. 4,-the`re isschematically illustrateda secondembodiment 20, indicated by broken lines, of

the' anti-ringing 'limiterof the present invention adapted forWoperationin conjunction with a transformer-coupled amplifier .stage foramplifying Va negative input pulse En, impressedonthe inputA ofamplifying element 2 supplied with powerwfrom a Bfsupply, not shown,through the primary ,of transformer 3' to produce .a lcorrespondingnegative output pulse 'Bout across the secondary of the transformer.Amplifying element 2, which may be any form of` amplifier unit,isrepresented herein as av PNP type transistor connected as illustrated toinduce a negative current pulse through the primary winding oftransformer Sfin response to the negative voltage pulse Em appliedto thebase region thereof.

Anti-ringing limiter 1 is connected across the primary Vwinding ofytransformery 3 and is operative to critically Y fdampthe inductivecircuit represented by transformer 3 andto `limitj'the amplitude of theprimary or positive voltage ypulse developedacross thej primarywindingof the transformer in response to the'leading edge of eachcurrentpulse forced'therethrough. v

Referring now toFig. 4 there is shown an embodiment of anti-ringinglimiter 1 which -is adapted for limiting primary positive .pulsesanddamping subsequent nega-l tive ringing pulses produced in winding 3 byamplifier `elementl inresponseto the application of negativepulse('Ei'n') to the input fof amplifier element 2. Since as indicated inFig. 4 the desired primaryvoltage pulse and the undesired ringingpulsewill be opposite inpolarity to the corresponding primary and ringingpulses'indicated in connection with Fig.V l,` it is clear that in theembodiment would appear at `the identical points ofthe circuit, werelanti-ringing limiter 1 removed, are indicated by dotted lines. Since thewaveforms of Fig. 5 are symmetrical to the waveforms of Fig. 3, furtherexplanation of the waveform chart of Fig. 5 is not required.

What is claimed as new is:

1. In a pulse circuit including an inductor and means for passingthrough the inductor a current pulse whose rise and fall tends todevelop a rst polarity and a succeeding'second opposite polarity voltagepulse, respectively, across the inductor, an 4anti-ringing limitercoupled polarity voltage pulse to a predetermined value and for dampingthe development of the second polarity voltage pulse,` said anti-ringinglimiter comprising: a resistor hav- ,ingta'rst and a second terminal,said first terminal being coupled to one extremity of the inductor; anda Zener diode operable for passing current strongly in its backdirection whenever it is back-biased by a voltage equal to saidpredetermined level, said Zener diodebeing coupled between the secondterminal of said resistor `and the other extremity of the inductor forisolating said resistor from the inductor when the first polarityvoltage pulse is less Athan the predetermined level and for couplingsaid resistor to the inductor when the second polarity voltage isdeveloped and when the rst polarity voltage pulse exceeds saidpredetermined level. i

2. An anti-ringing limiter circuit coupled to aninductor for limiting toa predetermined level the amplitude of a first polarity voltage pulsedeveloped across the inductor in response to a current pulse passingtherethrough and for damping the inductor to reduce the development ofan opposite polarity ringing pulse across the inductor in response tothe same current pulse, said anti-ringing limiter circuit comprising: a`damping resistance element having a first and a second terminal, saidfirst terminal being coupled to one extremity of the inductor; and aZener diode connected between the second terminal of said resistanceelement and the other extremity of the inductor, said Zener diode beingpoled so as to be backbiased by the first polarity kvoltage pulse andforwardbiased by the opposite polarity ringing pulse and having a ZenerVbreakdown voltage equal to the predetermined level thereby permittingback-current conduction through said Zener diode when the amplitude ofthe first polarity voltage pulse exceeds said predetermined level.

3. An anti-ringing limiter coupled to an inductor for clamping at apredetermined amplitude levelthe rst voltage pulse developed across theinductor in'. response to they rise of a current pulseforcedtherethrough and for critically clampingl the inductor to reducefasecond opposite polarity ringing pulse developing across the inductor inresponse to the fall of the current pulse; said'limiter comprising: aresistor; coupling means connected between said resistor and theinductor and operative to couple said resistor across the inductor inresponseto the ringing pulse and operative in response to the firstvvoltage pulse to de-couple said'V resistor so long as the amplitude ofthe first voltage pulse is less than the predetermined amplitude levelandl to couple said resistor across the inductor when the amplitude of`said first voltage pulse is greater than said predetermined referencelevel.

4. The anti-ringing limiter defined in claim 3 wherein said limiterfurther includes a unidirectional current device shunt connected acrosssaid resistor, said` unidirectional current device being poled so as tobe forwardbiased by the first voltage pulse and back-biased by theringing voltage pulse. 5. lThe anti-ringing limiter `dened in claim 3wherein .saidjcoupling means includesa Zener diode intercoupled .between.one end, of said resistor` and an extremity of -said inductor and poledso as to be back-biased by the .first voltage pulse a'njd forward-biasedbythe ringing voltage pulse, said Zener diode having a back-biasbreakdown vOltage equal toY said predetermined-amplitude `level.: Y i

6.j A- damped;inductively-coupled amplifier circuit cou- `pledjtqa-jpotential source and-responsive to an applied gvoltagreginput pulseAfor amplifying the input pulse to produce a corresponding amplifieroutput pulse of a predetermined amplitude level; said amplifiercomprising: an inductor having first and second inductor terminals, saidfirst inductor terminal being connected to the potential source; anamplifying element havingra pair of input terminals for receiving theapplied voltage input pulse and an output terminal connected to thesecond inductor terminal, said amplifying element being operative inresponse to the single input voltage pulse for forcing a correspondingcurrent pulse through said inductor to thereby tend to cause a firstpolarity voltage pulse and a subsequent opposite polarity ringingvoltage pulse to be developed across said inductor; and an antiringinglimiter intercoupled between said first and second inductor terminals,said limiter including a Zener diode and a resistor connected in seriesacross said first and second inductor terminals, said Zener diode beingpoled so as to be back-biased by said first polarity voltage pulse andforward-biased by said ringing pulse and having a predetermined`back-bias breakdown voltage equal to-the predetermined amplitude level,whereby said limiter is operative to limit the amplitude of said firstpolarity voltage pulse to the predetermined amplitude level and to dampsaid ringing voltage pulse.

7. The damped inductively-coupled amplifier circuit defined in claim 6wherein said amplifying element is Va transistor having its collectorconnected to the second inductor terminal and wherein said anti-ringinglimiter further includes a unidirectional current device connectedacross said resistor and poled so as to be forward-biased by said irstpolarity voltage pulse and back-biased by said ringing voltage pulse. Al

8. The damped inductively-coupled amplifier circuit defined in claim 7wherein said resistor has a predetermined resistance magnitude such thatthe ringing voltage pulse is substantially critically damped.

References Cited in the file of this patent UNITED STATES PATENTS2,594,336 Mohr Apr. V29, 1952 2,714,702 Shockley Aug.2, 1955 2,723,346Magnuson Nov.8, 1955 2,758,206 Hamilton Aug. 7, 1956 2,776,375 KeiperJan. l, 1957 2,809,339 Guggi Oct. 8, 1957

